Physicochemical properties of the soils associated with shifting cultivation in northern Thailand with special reference to factors determining soil fertility
1997
Funakawa, S. (Kyoto Prefectural Univ. (Japan). Faculty of Agriculture) | Tanaka, S. | Kaewkhongkha, T. | Hattori, T. | Yonebayashi, K.
Recently agricultural activity in the mountainous area of northern Thailand has increased and problems relating to soil fertility have arisen. In order to grain basic information about the soil properties associated with shifting cultivation, physicochemical properties of the surface soils (0-10cm) and subsoils (30-40cm) were investigated in selected villages in the area. The physicochemical properties of the soils studied are summarized as follows: 1) the soils were rich in organic matter, content of which ranged from 11.4 to 63.3 g C Kg(-1) in the surface soil. 2) The pH (H2O) of the soils mostly ranged from 5 to 7 and soil acidity was more pronounced in the deeper horizons. In the surface soils, exchangeable Ca and Mg were generally dominant, whereas exchangeable Al was often predominant in the subsoils. 3) Most of the soils showed a medium to fine texture with more than 30% clay. The clay mineral composition was characterized by various degrees of mixture of kaolin minerals and clay mica with, in some cases, a certain amount of 2:1-2:1:1 intergrades. 4) According to the ion adsorption curves, most of the B horizon soils were characterized by the predominance of permanent negative charges. On the other hand, organic matter contributed to the increase of variable negative charges in the surface soils. The content of organic matter and the percentage of the clay fraction were essential for determining the CEC of the soils of the surface 10 and 30-40cm depths, respectively. Thus, soil acidity both in the surface soils and subsoils, organic matter content in the surface soils,and clay content in the subsoils were considered to be the main factors that affected soil chemical fertility in the area
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